Experimental Extraction of Shared Secret Key from Fluctuations of Multipath Channel at Moving a Mobile Transceiver in an Urban Environment

Abstract

The Wireless Key Distribution is one of the most promising and fast growing areas in modern applied cryptography. This area covers various techniques of secure secret key distribution between two legitimate users who share a common radio channel with unpredictable signal fading in a multipath environment. In essence, the pair of legitimate nodes uses their multipath radio channel as a source of common randomness to establish a shared encryption key. There are a number of studies have been presented in recent publications devoted to experimental implementation of the Wireless Key Distribution using random variations in the received power of fading signal. Despite a number of valuable benefits, there is a much fewer experimental verifications of phase method with all of them are limited to a key distribution within some indoor environments only. Apparently, this is due to the technical difficulties of precise synchronization of legitimate users' equipment to provide coherent carrier phase measurements in a microwave radio frequency range. In this regard, our experiments can be considered as the first experimental verification of secure Wireless Key Distribution by observing random variations in the carrier phase of multipath signal at moving a mobile user within a real outdoor environment. To perform this, we used wireless Internet transmission of concurrent service data to maintain a required level of synchronization of one stationary and one mobile legal nodes. Despite the humble key generation rates we have achieved in practice, our results show possibility of secure wireless key distribution between the base station and mobile subscriber in a cellular communications scenario.